Various methods are known in the art for optical 3D mapping, i.e., generating a 3D profile of the surface of an object by processing an optical image of the object. This sort of 3D profile is also referred to as a depth map or depth image, and 3D mapping is also referred to as depth mapping.
Some methods of 3D mapping are based on projecting a laser speckle pattern onto the object, and then analyzing an image of the pattern on the object. For example, PCT International Publication WO 2007/043036, whose disclosure is incorporated herein by reference, describes a system and method for object reconstruction in which a coherent light source and a generator of a random speckle pattern project onto the object a coherent random speckle pattern. An imaging unit detects the light response of the illuminated region and generates image data. Shifts of the pattern in the image of the object relative to a reference image of the pattern are used in real-time reconstruction of a 3D map of the object. Further methods for 3D mapping using speckle patterns are described, for example, in PCT International Publication WO 2007/105205, whose disclosure is also incorporated herein by reference.
Other methods of optical 3D mapping project different sorts of patterns onto the object to be mapped. For example, PCT International Publication WO 2008/120217, whose disclosure is incorporated herein by reference, describes an illumination assembly for 3D mapping that includes a single transparency containing a fixed pattern of spots. A light source transilluminates the transparency with optical radiation so as to project the pattern onto an object. An image capture assembly captures an image of the pattern on the object, and the image is processed so as to reconstruct a 3D map of the object.
Still other methods of 3D mapping use a stereoscopic approach: Typically, two or more cameras at different positions capture respective images of the object. A computer analyzes the images to find the relative pixel offset of features of the object between the two images. The depths of the features are proportional to the respective offsets.
Automatic gain control (AGC) is used in many electronic imaging cameras. Various methods of AGC for such purposes are known in the art. For example, U.S. Pat. No. 5,712,682, whose disclosure is incorporated herein by reference, describes a system for generating a digital output signal representing a captured image. A sensor captures the image and generates a sensor output signal. A gain control amplifier is coupled to the sensor and receives the sensor output signal. The gain control amplifier has controls for applying various levels of gain to the sensor output signal. An analog-to-digital converter (ADC) is coupled to the gain control amplifier and generates the digital output signal representing the captured image. A processor, coupled to the ADC and the gain control amplifier, provides a control signal to the gain control amplifier for adjusting the level of gain applied by the amplifier.
As another example, U.S. Pat. No. 6,750,906, whose disclosure is incorporated herein by reference, describes an image processor system for a charge coupled device (CCD) or CMOS imaging system. The image processor system includes a histogram-based AGC circuit, which controls gain by adjusting the imaging system and adjusting a variable gain amplifier (VGA), as well as shutter timing for shutter gain.